1. Field of the Invention
The present invention relates generally to a radiation sensitive resin composition and to a material containing the composition for forming bumps. More particularly, the present invention relates to a radiation sensitive resin composition suitable for photofabrication of bumps when a circuit substrate is fabricated or when a semiconductor, an electronic component or the like is mounted on the circuit substrate as well as to a material containing such a radiation sensitive resin composition for forming bumps.
2. Description of the Related Art
Photofabrication is a generic name for a technology which fabricates various precision parts, the technology including coating a radiation sensitive resin composition on an article to be processed, patterning the coated film by photolithography, electroforming as by one or more of chemical etching, electrolytic etching or electroplating using the patterned film as a mask. The photofabrication is a technology which is leading the current precision microprocessing techniques.
Recently, down sizing of electronic apparatus and appliances is prevailing in accordance with which incessant change in the design of LSIs is on-going, that is, those LSIs which are more highly integrated or have more layers are fabricated. As a result, there is a demand for a multi-pin packaging method for mounting an LSI on a substrate in order to package the LSI on an electronic apparatus or appliance and attention has been focused on bare chip packaging such as a TAB method or a flip chip method. In such a multi-pin packaging method, it is necessary to arrange protruded electrodes of 20 .mu.m in height which serve as connector terminals called "bump" on a substrate with high precision. In future, a further down-sizing of LSI will invoke a need for an increasingly high precision of bumps.
Materials for use in forming such a bump are required to meet various requirements. For example, the materials must be able to form a thick film as thick as 20 .mu.m or more, must have enough adhesion to the substrate, must have sufficient resistance and wettability to plating liquids, and must be readily peeled with a peeling liquid after the plating is over.
Further, a film coated from the materials for use in forming such a bump must have a sufficient flexibility when the film is coated on a flexible substrate such as a polyimide film or the like. This is because no crack should occur in the resulting film even when the substrate is bent to some extent.
However, a resist, which is a conventional material for forming bumps, is insufficient in its adhesion to a substrate and wettability to plating liquids.
Accordingly, when the resist has poor adhesion to the substrate upon development, a problem occurs that use of finer pattern sizes of the resist for forming bumps causes a problem that the resist tends to come off the substrate more often.
In addition, another problem arises that when the material for forming bumps has a poor wettability to plating liquids, no uniform plating can be formed on the substrate.